The present invention relates to a catalyst for the synthesis of chlorine dioxide and to a method of making such a catalyst. The catalyst is preferably palladium, or palladium together with another platinum group metal (e.g., Pd+Pt), or palladium together with a Group IB metal (e.g., Pd+Au) deposited on a support consisting of a Group IA carbonate salt (e.g., K2CO3) or a Group IIA carbonate salt (e.g., CaCO3) or a magnesium salt that can be converted to MgO or a support modified by Group IA carbonate salt (e.g., K2CO3) or a Group IIA carbonate salt (e.g., CaCO3) or a magnesium salt that can be converted to MgO. The catalysts of the present invention has a slower rate of deactivation than catalysts previously used for this purpose.
In another aspect, the present invention concerns a method for generating chlorine dioxide from an aqueous solution of a precursor therefor and directing the resulting chlorine dioxide at the material to be disinfected.
Chlorine dioxide is known to act as a disinfecting or sterilizing agent for solutions and devices (e.g., contact lenses). Chlorine dioxide is generally produced from a solution of a chlorine dioxide precursor, such as sodium chlorite solutions, by contacting the solution with a catalyst (e.g., catalysts containing noble metals, as described for example in U.S. Pat. No. 5,008,096). However, known catalysts have the disadvantage of becoming greatly deactivated within a matter of days.
An object of the present invention is to provide novel chlorine dioxide generating catalysts having a slower rate of deactivation than known catalysts. In achieving the above and other objects, one feature of the invention resides in a catalyst which is composed of a support wherein the outside edge of the support is impregnated with palladium or palladium and another platinum group metal or palladium and a Group IB metal. The support itself is selected from the group of supports modified by a Group IA carbonate salt or a Group IIA carbonate salt or a magnesium salt that can be converted to MgO. Many well known catalyst supports, such as gamma alumina, can be used to form the modified support as described. In another aspect, the Group IA carbonate salt (e.g., K2CO3) or Group IIA carbonate salt (e.g., CaCO3) or a magnesium salt that can be converted to MgO can be formed into a self sustaining support such as a pellet or honeycomb.
Another object of the present invention is to provide a method of making a catalyst for producing chlorine dioxide having a slower rate of deactivation. The method involves preadjusting the pH of an aqueous solution of palladium or palladium and another platinum group metal or palladium and a Group IB metal salt to a pH range of 1 to 6.3, adding the solution to a slurry of water and a support selected from supports modified by a Group IA carbonate salt or a Group IIA carbonate salt or a magnesium salt that can be converted to MgO or a support consisting of a Group IA carbonate salt (e.g., K2CO3) or a Group IIA carbonate salt (e.g., CaCO3) or a magnesium salt that can be converted to MgO, maintaining the pH of the slurry from 6 to 10 for several minutes at a temperature of 70xc2x0 to 90xc2x0 C., and adding a reducing agent, thereby impregnating the outside edge of the support with palladium or palladium and another platinum group metal or palladium and a Group IB metal.
An additional object of the present invention is to provide a method for generating chlorine dioxide from a chlorine dioxide precursor. The method involves contacting an aqueous medium containing a chlorine dioxide precursor with the above described catalyst.
Another method for generating chlorine dioxide from a chlorine dioxide precursor involves providing a multicompartment container, a first compartment containing a chlorine dioxide precursor, a second compartment containing the catalyst described above, dispelling from the first compartment a quantity of the chlorine dioxide precursor to flow into the second compartment containing the catalyst, contacting the precursor with the catalyst thereby forming chlorine dioxide, and ejecting the chlorine dioxide from the container to the surface of an item to be disinfected or treated.
Furthermore, there is provided a two component package comprising the catalyst described above and a chlorine dioxide precursor.